High transmission light control film

ABSTRACT

A light control film, comprises a light input surface and alight output surface opposite the light input surface. Alternating transmissive regions and absorptive regions are disposed between the light input surface and the light output surface. The absorptive regions have an aspect ratio of at least 30 and the alternating transmissive region and absorptive regions have a relative transmission at a viewing angle of 0 degrees of at least 75%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a cross-sectional view of an embodied light control film.

FIG. 1b depicts the polar cut-off viewing angle of the light control film of FIG. 1 a.

FIG. 2 is a perspective view of a microstructured film.

FIG. 3 is a cross-sectional schematic of an embodied method of making a light control film.

FIG. 4 is a perspective view of a light control film further comprising a cover film bonded with an adhesive layer.

FIG. 5 is a perspective schematic of a backlit display comprising an embodied light control film.

FIG. 6 is a plot of luminance versus viewing angle for various light control films.

SUMMARY

Although various light control films have been described, industry would find advantage in light control films suitable for use as a privacy film having improved properties such as improved on-axis transmission.

In one embodiment, a light control film is described comprising a light input surface and a light output surface opposite the light input surface and alternating transmissive regions and absorptive regions disposed between the light input surface and the light output surface.

In one embodiment, the absorptive regions have an aspect ratio of at least 30 and the alternating transmissive region and absorptive regions have a relative transmission at a viewing angle of 0 degrees of at least 75%.

In another embodiment, the absorptive regions have an aspect ratio of at least 30 and comprise an organic light absorptive material.

In another embodiment, the absorptive regions comprise a plurality of particles having a median particle size of less than 100 nanometers.

In another embodiment, the absorptive regions comprise a polyelectrolyte.

In some embodiments, the light control film further comprises additional layers such as a topcoat or adhesive and cover film and the total light control film has specified transmission properties as described herein.

In another embodiment, the light control film comprises a first light control film as just described disposed upon a second light control film. The second light control film may also have absorptive regions have an aspect ratio of at least 30.

In yet another embodiment, a method of making a light control film is described comprising: providing a microstructured film comprising a plurality of light transmissive regions alternated with channels, wherein the microstructured film has a surface defined by a top surface and side walls of the light transmissive regions and a bottom surface of the channels; applying an organic light absorptive material to the surface, and removing at least a portion of the light absorptive coating from the top surface of the light transmissive regions and bottom surface of the channels.

In yet another embodiment, a method of making a microstructured film is described comprising: providing a microstructured film comprising a plurality of light transmissive regions alternated with channels, wherein the microstructured film has a surface defined by a top surface and side walls of the light transmissive regions and a bottom surface of the channels; applying a light absorptive material to the surface by layer-by-layer self-assembly; removing at least a portion of the light absorptive coating from the top surface of the light transmissive regions and bottom surface of the channels.

DETAILED DESCRIPTION

In one embodiment, a light control film (“LCF”) is described. With reference to FIG. 1a , a cross-sectional view of an embodied LCF 100, the LCF comprises a light output surface 120 and an opposing light input surface 110. The light output surface 120 is typically parallel to the light input surface 110. LCF 100 includes alternating transmissive regions 130 and absorptive regions 140 disposed between the light output surface 120 and a light input surface 110.

In one embodiment, as depicted in FIG. 1a , the transmissive regions 130 are typically integral with a land region “L”, meaning that there is no interface between the land region and the base portion 131 of the transmissive regions 130. Alternatively, LCF may lack such land region L or an interface may be present between the land region, L, and transmissive regions 130. In this embodiment, the land region is disposed between the alternating transmissive regions 130 and absorptive regions 140 and light input surface 110.

Alternatively, in another embodiment, surface 120 may be the light input surface and surface 110 may be the light output surface. In this embodiment, the land region is disposed between the alternating transmissive regions 130 and absorptive regions 140 and light output surface.

The transmissive regions 130 can be defined by a width “W_(T)”. Excluding the land region “L”, the transmissive regions 130 typically have nominally the same height as the absorptive regions 140. In typical embodiments, the height of the absorptive regions, H_(A), is at least 30, 40, 50, 60, 70, 80, 90 or 100 microns. In some embodiments, the height is no greater than 200, 190, 180, 170, 160, or 150 microns. In some embodiments, the height is no greater than 140, 130, 120, 110, or 100 microns. The LCF typically comprises a plurality of transmissive regions having nominally the same height and width. In some embodiments, the transmissive regions have a height, “H_(T)”, a maximum width at its widest portion, “W_(T)”, and an aspect ratio, H_(T)/W_(T), of at least 1.75. In some embodiments, H_(T)/W_(T) is at least 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0. In other embodiments, the aspect ratio of the transmissive regions is at least 6, 7, 8, 9, 10. In other embodiments, the aspect ratio of the transmissive regions is at least 15, 20, 25, 30, 35, 40, 45, or 50.

Absorptive regions 140 have a height “H_(A)” defined by the distance between the bottom surface 155 and top surface 145, such top and bottom surfaces typically being parallel to the light output surface 120 and a light input surface 110. The absorptive regions 140 have a maximum width W_(A) and are spaced apart along surface light output surface 120 by a pitch “P_(A)”.

The width of the absorptive regions, “W_(A)”, at the base (i.e. adjacent to bottom surface 155) is typically nominally the same as the width of the absorptive regions adjacent the top surface 145. However, when the width of the absorptive regions at the base differs from the width adjacent the top surface, the width is defined by the maximum width. The maximum width of a plurality of absorptive regions can be averaged for an area of interest, such as an area in which the transmission (e.g. brightness) is measured. The LCF typically comprises a plurality of absorptive regions having nominally the same height and width. In typical embodiments, the absorptive regions generally have a width no greater than 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 micron. In some embodiments, the absorptive regions generally have a width no greater than 900, 800, 700, 600, or 500 nanometers. In some embodiments, the absorptive regions have a width of at least 50, 60, 70, 80, 90, or 100 nanometers.

An absorptive region can be defined by an aspect ratio, the height of the absorptive region divided by the maximum width of the absorptive region (HA/WA). In some embodiments, the aspect ratio of the absorptive regions is at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. In favored embodiments, the height and width of the absorptive region(s) are selected such that the absorptive region(s) have an even higher aspect ratio. In some embodiments, the aspect ratio of the absorptive regions is at least 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100. In other embodiments, the aspect ratio of the absorptive regions is at least 200, 300, 400, or 500. The aspect ratio can range up to 10,000 or greater. In some embodiments, the aspect ratio is no greater than 9,000; 8,000; 7,000; 6,000, 5,000; 4,000, 3000; 2,000, or 1,000.

As shown in FIG. 1b , LCF 100 includes alternating transmissive regions 130 and absorptive regions 140, and an interface 150 between transmissive regions 130 and absorptive regions 140. Interface 150 forms a wall angle θ with line 160 that is perpendicular to light output surface 120.

Larger wall angles θ decrease transmission at normal incidence or in other words a viewing angle of 0 degrees. Smaller wall angles are preferred such that the transmission of light at normal incidence can be made as large as possible. In some embodiments, the wall angle θ is less than 10, 9, 8, 7, 6, or 5 degrees. In some embodiments, the wall angle is no greater than 2.5, 2.0. 1.5, 1.0, 0.5, or 0.1 degrees. In some embodiments, the wall angle is zero or approaching zero. When the wall angle is zero, the angle between the absorptive regions and light output surface 120 is 90 degrees. Depending on the wall angle, the transmissive regions can have a rectangular or trapezoidal cross-section.

The transmission (e.g. brightness of visible light) can be increased when incident light undergoes total internal reflection (TIR) from the interface between the absorptive and transmissive regions. Whether a light ray will undergo TIR or not, can be determined from the incidence angle with the interface, and the difference in refractive index of the materials of the transmissive and absorptive regions.

As shown in FIG. 1b , transmissive regions 130 between absorptive regions 140 have an interface angle θ_(I) defined by the geometry of alternating transmissive regions 130 and absorptive regions. As depicted in FIGS. 1a and 1b , the interface angle θ_(I) can be defined by the intersection of two lines. The first line extends from a first point, defined by the bottom surface and the side wall surface of a first absorptive region, and a second point defined by the top surface and side wall surface of the nearest second absorptive region. The second line extends from a first point defined, by the top surface and the side wall surface of the first absorptive region, and a second point, defined by the bottom surface and side wall surface of the second absorptive region.

The polar cut-off viewing angle θP is equal to the sum of a polar cut-off viewing half angle θ1 and a polar cut-off viewing half angle θ2 each of which are measured from the normal to light input surface 110. In typical embodiments, the polar cut-off viewing angle θP is symmetric, and polar cut-off viewing half angle θ1 is equal to polar viewing half angle θ2. Alternatively, the polar cut-off viewing angle θP can be asymmetric, and polar cut-off viewing half angle θ1 is not equal to polar cut-off viewing half angle θ2.

Luminance can be measured according to the test method described in the examples. The luminance can be measured on the alternating transmissive and absorptive regions, such as illustrated in FIG. 1a or the total light control film that may further comprise a cover film, such as illustrated in FIG. 4. Relative transmission (e.g. brightness of visible light) is defined as the percentage of luminance, at a specified viewing angle or range of viewing angles, between a reading with the light control film including the alternating transmissive and absorptive regions and optionally other layers and a reading without the light control film (i.e. the baseline). With reference to FIG. 6, the viewing angle can range from −90 degrees to +90 degrees. A viewing angle of 0 degrees is orthogonal to light input surface 110; whereas viewing angles of −90 degrees and +90 degrees are parallel to light input surface 110.

For example, with reference to FIG. 6, the on-axis baseline luminance is 2100 Cd/m². EX. 6 has an on-axis luminance of 1910 Cd/m². Thus, the relative transmission (e.g. brightness) is 1910 Cd/m²/2100 Cd/m² multiplied by 100, which equals 91.0%. Unless specified otherwise, the relative transmission refers to the relative transmission of visible light having a 400-700 nm wavelength range as measured by the test method described in further detail in the examples.

The alternating transmissive and absorptive regions or total LCF can exhibit increased relative transmission (e.g. brightness) at a viewing angle of 0 degrees. In some embodiments, the relative transmission (e.g. brightness) is at least 75, 80, 85, or 90%. The relative transmission (e.g. brightness) is typically less than 100%. In typical embodiments, the LCF has significantly lower transmission at other viewing angles. For example, in some embodiments, the relative transmission (e.g. brightness) at a viewing angle of −30 degrees, +30 degrees, or an average of −30 degrees and +30 degrees is less than 50, 45, 40, 35, 30, or 25%. In other embodiments, the relative transmission (e.g. brightness) at a viewing angle of 30 degrees, +30 degrees, or the average of −30 degrees and +30 degrees is less than 25, 20, 15, 10 or 5%. In some embodiments, the relative transmission (e.g. brightness) at a viewing angle of +/−35, +/−40, +/−45, +/−50, +/−55, +/−60, +/−65, +/−70, +/−75, or +/−80 degrees is less than 25, 20, 15, 10 or 5%, or less than 5%. In some embodiments, the average relative transmission (e.g. brightness) for viewing angles ranging from +35 to +80 degrees, −35 to −80 degrees, or the average of these ranges is less than 10, 9, 8, 7, 6, 5, 4, 3, or 2%.

LCFs with significantly lower transmission at “off-axis” viewing angles are suitable for use as privacy films. Such films allow a viewer directly in front of a display (viewing angle of 0 degrees) to see the image, yet blocks viewers at “off-axis” angles from seeing such image.

The absorptive regions can be formed by coating the surface of a microstructured film. FIG. 2 shows an embodied microstructured film article 200 that can be coated to make a LCF. The depicted microstructured film includes a microstructured surface 210 comprising a plurality of channels 201 a-201 d on base layer 260. As shown in FIG. 2, a continuous land layer “L” can be present between the bottom of the channels 205 and the top surface 210 of base layer 260 to base layer 260. Alternatively, the channels 201 can extend all the way through the microstructured film article 200. In this embodiment (not shown), the bottom surface 205 of the groove can be coincident with the top surface 210 of a base layer 260. In typical embodiments, the base layer 260 is a preformed film that comprises a different organic polymeric material than the transmissive regions 230 as will subsequently be described.

The height and width of protrusions (e.g. transmissive regions) 230 are defined by adjacent channels (e.g. 201 a and 201 b). The protrusions (e.g. transmissive regions) 230 can be defined by a top surface 220, a bottom surface, 231, and side walls 232 and 233 that join the top surface to the bottom surface. The side walls can be parallel to each other. More typically the side walls have a wall angle as previously described.

In some embodiments, the protrusions (e.g. transmissive regions) 230 have a pitch, “P_(T)” of at least 10 microns. The pitch is the distance between the onset of a first protrusion (e.g. transmissive region) and the onset of a second protrusion (e.g. transmissive region) as depicted in FIG. 2. The pitch may be at least 15, 20, 25, 30, 35, 40, 45, or 50 microns. The pitch is generally no greater than 1 mm. The pitch is typically no greater than 900, 800, 700, 600, or 500 microns. In some embodiments, the pitch is typically no greater than 550, 500, 450, 400, 350, 300, 250 or 200 microns. In some embodiments, the pitch is no greater than 175, 150, 100 microns. In typical embodiments, the protrusions are evenly spaced, having a single pitch. Alternatively, the protrusions may be spaced such that the pitch between adjacent protrusions is not the same. In this later embodiment, at least some and typically the majority (at least 50, 60, 70, 80, 90% or greater of the total protrusions) have the pitch just described.

The pitch of the absorptive regions P_(A) is within the same range as just described for the light transmissive regions.

The pitch and height of the protrusions (e.g. transmissive regions) can be important to facilitate coating of the protrusions (e.g. transmissive regions) with a light absorbing coating. When the protrusions are spaced too close together it can be difficult to uniformly coat the side walls. When the protrusions are spaced too far apart, the light absorbing coating may not be effective at providing its intended function, such as privacy at off-axis viewing angles.

The absorptive regions are formed by providing a light absorptive coating on the side walls of protrusions (e.g. transmissive regions) of a microstructured film. The thickness of the light absorptive coating is equivalent to the width of the absorptive regions, W_(A), as previously described. The absorptive regions can be formed by any method that provides a sufficiently thin, conformal, light absorptive coating on the side walls (e.g. 232, 233).

In one embodiment, the absorptive regions are formed by a combination of additive and subtractive methods.

With reference to FIG. 3, the light control film can be prepared by providing a microstructured film 300 (such as the microstructured film of FIG. 2) comprising a plurality of protrusions (e.g. transmissive regions) defined by a top surface (e.g. 320) and side walls (332, 333). The plurality of protrusions (e.g. transmissive regions) 330 are separated from each other by channels 301 a and 301 b. The side walls of the protrusions (e.g. transmissive regions) are coincident with the side walls of the channels. The channels further comprise a bottom surface 305 that is parallel to or coincident with top surface of base layer 360. The method further comprises applying a light absorptive coating 341 to the (e.g. entire) surface of the microstructured film, i.e. the top surface 320 and side walls 332, 333 of the protrusions (e.g. transmissive regions) and the bottom surface 305 of the channels that separate the protrusions (e.g. transmissive regions). The method further comprises removing the coating from the top surface 320 of the protrusions (e.g. transmissive regions) and bottom surface 305 of the channels. In some embodiments, the method further comprises filling the channels with an organic polymeric material 345 such as (e.g. the same) polymerizable resin as the protrusions (e.g. transmissive regions) and curing the polymerizable resin. When the channels are not filled with a cured polymerizable resin, the channels are typically filled with air.

A microstructure-bearing article (e.g. microstructured film article 200 shown in FIG. 2) can be prepared by any suitable method. In one embodiment, the microstructure-bearing article (e.g. microstructured film article 200 shown in FIG. 2) can be prepared by a method including the steps of (a) preparing a polymerizable composition; (b) depositing the polymerizable composition onto a master negative microstructured molding surface (e.g. tool) in an amount barely sufficient to fill the cavities of the master; (c) filling the cavities by moving a bead of the polymerizable composition between a (e.g. preformed film) base layer and the master, at least one of which is flexible; and (d) curing the composition. The deposition temperature can range from ambient temperature to about 180° F. (82° C.). The master can be metallic, such as nickel, chrome- or nickel-plated copper or brass, or can be a thermoplastic material that is stable under the polymerization conditions, and has a surface energy that allows clean removal of the polymerized material from the master. When the base layer is a preformed film, one or more of the surfaces of the film can optionally be primed or otherwise be treated to promote adhesion with the organic material of the light transmissive regions.

The polymerizable resin can comprise a combination of a first and second polymerizable component selected from (meth)acrylate monomers, (meth)acrylate oligomers, and mixtures thereof. As used herein, “monomer” or “oligomer” is any substance that can be converted into a polymer. The term “(meth)acrylate” refers to both acrylate and methacrylate compounds. In some cases, the polymerizable composition can comprise a (meth)acrylated urethane oligomer, (meth)acrylated epoxy oligomer, (meth)acrylated polyester oligomer, a (meth)acrylated phenolic oligomer, a (meth)acrylated acrylic oligomer, and mixtures thereof.

The polymerizable resin can be a radiation curable polymeric resin, such as a UV curable resin. In some cases, polymerizable resin compositions useful for the LCF of the present invention can include polymerizable resin compositions such as are described in U.S. Pat. No. 8,012,567 (Gaides et al.), to the extent that those compositions satisfy the index and absorption characteristics herein described.

The chemical composition and thickness of the base layer can depend on the end use of the LCF. In typical embodiments, the thickness of the base layer can be at least about 0.025 millimeters (mm) and can be from about 0.05 mm to about 0.25 mm.

Useful base layer materials include, for example, styrene-acrylonitrile, cellulose acetate butyrate, cellulose acetate propionate, cellulose triacetate, polyether sulfone, polymethyl methacrylate, polyurethane, polyester, polycarbonate, polyvinyl chloride, polystyrene, polyethylene naphthalate, copolymers or blends based on naphthalene dicarboxylic acids, polyolefin-based material such as cast or orientated films of polyethylene, polypropylene, and polycyclo-olefins, polyimides, and glass. Optionally, the base layer can contain mixtures or combinations of these materials. In some embodiments, the base layer may be multi-layered or may contain a dispersed component suspended or dispersed in a continuous phase.

Examples of base layer materials include polyethylene terephthalate (PET) and polycarbonate (PC). Examples of useful PET films include photograde polyethylene terephthalate, available from DuPont Films of Wilmington, Del. under the trade designation “Melinex 618”. Examples of optical grade polycarbonate films include LEXAN® polycarbonate film 8010, available from GE Polymershapes, Seattle Wash., and Panlite 1151, available from Teijin Kasei, Alpharetta Ga.

Some base layers can be optically active, and can act as polarizing materials. Polarization of light through a film can be accomplished, for example, by the inclusion of dichroic polarizers in a film material that selectively absorbs passing light. Light polarization can also be achieved by including inorganic materials such as aligned mica chips or by a discontinuous phase dispersed within a continuous film, such as droplets of light modulating liquid crystals dispersed within a continuous film. As an alternative, a film can be prepared from microtine layers of different materials. The polarizing materials within the film can be aligned into a polarizing orientation, for example, by employing methods such as stretching the film, applying electric or magnetic fields, and coating techniques.

Examples of polarizing films include those described in U.S. Pat. No. 5,825,543 (Ouderkirk et al.); U.S. Pat. No. 5,783,120 (Ouderkirk et al.); U.S. Pat. No. 5,882,774 (Jonza et al.); U.S. Pat. No. 5,612,820 (Shrenk et al.) and U.S. Pat. No. 5,486,949 (Shrenk et al.). The use of these polarizer films in combination with prismatic brightness enhancement film has been described, for example, in U.S. Pat. No. 6,111,696 (Allen et al.) and U.S. Pat. No. 5,828,488 (Ouderkirk et al.). Films available commercially are multilayer reflective polarizer films such as 3M™ Dual Brightness Enhancement Film “DBEF”, available from 3M Company.

In some embodiments, the base layer is a multilayer film that imparts a color shifting effect such as described in U.S. Pat. No. 8,503,122. Suitable color shifting films are described in U.S. Pat. No. 6,531,230 to Weber et al.; incorporated herein by reference.

Other suitable color shifting films include multilayer films generated by spin coating, blade coating, dip coating, evaporation, sputtering, chemical vapor deposition (CVD), and the like. Exemplary films include both organic and inorganic materials. Such films are described, for instance, in U.S. Pat. Nos. 7,140,741; 7,486,019; and 7,018,713. Alternatively, the microstructure-bearing article (e.g. microstructured film article 200 shown in FIG. 2) can be prepared by melt extrusion, i.e. casting a fluid resin composition onto a master negative microstructured molding surface (e.g. tool) and allowing the composition to harden. In this embodiment, the protrusions (e.g. light transmissive regions) are interconnected in a continuous layer to base layer 260. The individual protrusions (e.g. light transmissive regions) and connections therebetween generally comprises the same thermoplastic material. The thickness of the land layer (i.e. the thickness excluding that portion resulting from the replicated microstructure) is typically between 0.001 and 0.100 inches and preferably between 0.003 and 0.010 inches.

Suitable resin compositions for melt extrusion are transparent materials that are dimensionally stable, durable, weatherable, and readily formable into the desired configuration. Examples of suitable materials include acrylics, which have an index of refraction of about 1.5, such as Plexiglas brand resin manufactured by Rohm and Haas Company; polycarbonates, which have an index of refraction of about 1.59; reactive materials such as thermoset acrylates and epoxy acrylates; polyethylene based ionomers, such as those marketed under the brand name of SURLYN by E. I. Dupont de Nemours and Co., Inc.; (poly)ethylene-co-acrylic acid; polyesters; polyurethanes; and cellulose acetate butyrates. Polycarbonates are particularly suitable because of their toughness and relatively higher refractive index.

In yet another embodiment, the master negative microstructured molding surface (e.g. tool) can be employed as an embossing tool, such as described in U.S. Pat. No. 4,601,861 (Pricone).

The absorptive regions are generally formed by coating the surface of a microstructured film. Various coating methods can be used including for example layer-by-layer (LbL) coating, vapor deposition, sputtering, reactive sputtering and atomic layer deposition (ALD).

Light absorbing materials useful for forming light absorbing regions can be any suitable material that functions to absorb or block light at least in a portion of the visible spectrum. Preferably, the light absorbing material can be coated or otherwise provided on the side walls of the light transmissive regions to form light absorbing regions in the LCF. Exemplary light absorbing materials include a black or other light absorbing colorant (such as carbon black or another pigment or dye, or combinations thereof). Other light absorbing materials can include particles or other scattering elements that can function to block light from being transmitted through the light absorbing regions.

When the light absorbing material (e.g. coating) includes particles, the particles have a median particle size D50 equal to or less than the thickness of the light absorbing material (e.g. coating) or in other words substantially less than the width of the absorptive regions WA.

The median particle size is generally less than 1 micron. In some embodiments, the median particle size is no greater than 900, 800, 700, 600, or 500 nm. In some embodiments, the median particle size is no greater than 450, 400, 350, 300, 250, 200, or 100 nm. In some embodiments, the median particle size is no greater than 90, 85, 80, 75, 70, 65, 60, 55, or 50 nm. In some embodiments, the median particle size is no greater than 30, 25, 20, or 15 nm. The median particle size is typically at least 1, 2, 3, 4, or 5 nanometers. The particle size of the nanoparticles of the absorptive regions can be measured using transmission electron microscopy or scanning electron microscopy, for example.

“Primary particle size” refers to the median diameter of a single (non-aggregate, non-agglomerate) particle. “Agglomerate” refers to a weak association between primary particles which may be held together by charge or polarity and can be broken down into smaller entities. As used herein “aggregate” with respect to particles refers to strongly bonded or fused particles where the resulting external surface area may be significantly smaller than the sum of calculated surface areas of the individual components. The forces holding an aggregate together are strong forces, for example covalent bonds, or those resulting from sintering or complex physical entanglement. Although agglomerated nanoparticles can be broken down into smaller entities such as discrete primary particles such as by application of a surface treatment; the application of a surface treatment to an aggregate simply results in a surface treated aggregate. In some embodiments, a majority of the nanoparticles (i.e. at least 50%) are present as discrete unagglomerated nanoparticles. For example, at least 70%, 80% or 90% of the nanoparticles (e.g. of the coating solution) are present as discrete unagglomerated nanoparticles.

The concentration of light absorbing nanoparticles is typically at least 10, 15, 20, 25, 30, 35, 40, 45, or 50 wt.-% of the total light absorptive region. In some embodiments, the concentration of light absorbing nanoparticles is at least 55, 60, 65, 70, or 75 wt.-% of the total light absorptive regions. The concentration of light absorbing nanoparticles can be determined by methods known in the art, such as thermogravimetric analysis.

In one embodiment, the method comprises applying a layer-by layer light absorptive coating to the surface of the microstructured film, i.e. the top surface and side walls of the protrusions and bottom surface of the channels.

In some embodiments, the plurality of layers disposed on the surface of the microstructured film comprise at least two layers deposited by what is commonly referred to as a “layer-by-layer self-assembly process”. This process is commonly used to assemble films or coatings of oppositely charged polyelectrolytes electrostatically, but other functionalities such as hydrogen bond donor/acceptors, metal ions/ligands, and covalent bonding moieties can be the driving force for film assembly. “Polyelectrolyte” means a polymer or compound with multiple ionic groups capable of electrostatic interaction. “Strong polyelectrolytes” possess permanent charges across a wide range of pH (e.g., polymers containing quaternary ammonium groups or sulfonic acid groups). “Weak polyelectrolytes” possess a pH-dependent level of charge (e.g. polymers containing primary, secondary, or tertiary amines, or carboxylic acids). Typically, this deposition process involves exposing the substrate having a surface charge, to a series of liquid solutions, or baths. This can be accomplished by immersion of the substrate into liquid baths (also referred to as dip coating), spraying, spin coating, roll coating, inkjet printing, and the like. Exposure to the first polyion (e.g. polyelectrolyte bath) liquid solution, which has charge opposite that of the substrate, results in charged species near the substrate surface adsorbing quickly, establishing a concentration gradient, and drawing more polyelectrolyte from the bulk solution to the surface. Further adsorption occurs until a sufficient layer has developed to mask the underlying charge and reverse the net charge of the substrate surface. In order for mass transfer and adsorption to occur, this exposure time is typically on the order of minutes. The substrate is then removed from the first polyion (e.g. bath) liquid solution, and is then exposed to a series of water rinse baths to remove any physically entangled or loosely bound polyelectrolyte. Following these rinse (e.g. bath) liquid solutions, the substrate is then exposed to a second polyion (e.g. polyelectrolyte or inorganic oxide nanoparticle bath) liquid solution, which has charge opposite that of the first polyion (e.g. bath) liquid solution. Once again adsorption occurs, since the surface charge of the substrate is opposite that of the second (e.g. bath) liquid solution. Continued exposure to the second polyion (e.g. bath) liquid solution then results in a reversal of the surface charge of the substrate. A subsequent rinsing can be performed to complete the cycle. This sequence of steps is said to build up one layer pair, also referred to herein as a “bi-layer” of deposition and can be repeated as desired to add further layer pairs to the substrate.

Some examples of suitable processes include those described in Krogman et al., U.S. Pat. No. 8,234,998; Hammond-Cunningham et al., US2011/0064936; and Nogueira et al., U.S. Pat. No. 8,313,798. Layer-by layer dip coating can be conducted using a StratoSequence VI (nanoStrata Inc., Tallahassee, Fla.) dip coating robot.

In one embodiment, the plurality of layers deposited by layer-by-layer self-assembly is a polyelectrolyte stack comprising an organic polymeric polyion (e.g. cation) and counterion (e.g. anion) comprising a light absorbing material (e.g. pigment). At least a portion of the cation layers, anion layers, or a combination thereof comprise a light absorbing material (e.g. pigment) ionically bonded to the polyelectrolyte.

The thickness of a bi-layer and the number of bi-layers are selected to achieve the desired light absorption. In some embodiments, the thickness of a bi-layer, the number of bi-layers are selected to achieve the desired (e.g. absorption) optical properties using the minimum total thickness of self-assembled layers and/or the minimum number of layer-by-layer deposition steps. The thickness of each bi-layer typically ranges from about 5 nm to 350 nm. The number of bi-layers is typically at least 5, 6, 7, 8, 9, or 10. In some embodiments, the number of bilayers per stack is no greater than 150 or 100. The thickness of a stack is equivalent to the width of the absorptive regions W_(A), as previously described.

A light absorbing compound is dispersed within at least a portion of the polyelectrolyte layers. Various polyelectrolytes can be utilized including inorganic compounds, such as silica or silicate, as well as various phosphonocarboxylic acids and salts thereof (some of which are described in WO2015/095317; incorporated herein by reference.)

Polyelectrolyte organic polymers can be preferred since such materials can be more easily removed by reactive ion etching than inorganic materials.

Suitable polycationic organic polymers include, but are not limited to linear and branched poly(ethylenimine) (PEI), poly(allylamine hydrochloride), polyvinylamine, chitosan, polyaniline, polyamidoamine, poly(vinylbenzyltriamethylamine), polydiallyldimethylammonium chloride (PDAC), poly(dimethylaminoethyl methacrylate), poly(methacryloylamino)propyl-trimethylammonium chloride, and combinations thereof including copolymers thereof.

Suitable polyanionic organic polymers include, but are not limited to, poly(vinyl sulfate), poly(vinyl sulfonate), poly(acrylic acid) (PAA), poly(methacrylic acid), poly(styrene sulfonate), dextran sulfate, heparin, hyaluronic acid, carrageenan, carboxymethylcellulose, alginate, sulfonated tetrafluoroethylene based fluoropolymers such as Nafion®, poly(vinylphosphoric acid), poly(vinylphosphonic acid), and combinations thereof including copolymers thereof.

The molecular weight of the polyelectrolyte polymers can vary, ranging from about 1,000 g/mole to about 1,000,000 g/mole. In some embodiments, the molecular weight (Mw) of the (e.g. poly(acrylic acid)) negatively charged anionic layer ranges from 50,000 g/mole to 150,000 g/mole. In some embodiments, the molecular weight (Mw) of the (e.g. polydiallyldimethylammonium chloride) positively charged cationic layer ranges from 50,000 g/mole to 300,000 g/mole. In some embodiments, the molecular weight (Mw) of the (e.g. poly(ethyleneimine) positively charged cationic layer ranges from 10,000 g/mole to 50,000 g/mole.

At least one of the polyions (e.g. the polyanion or polycation) comprises a light absorbing material.

In order to be stable in water as a colloidal dispersion and impart polyionic groups, the light absorbing (e.g. pigment) particles typically further comprise an ionic surface treatment. In some embodiments, the surface treatment compound is anionic, such as in the case of sulfonate or carboxylate. The light absorbing (e.g. pigment) particles also function as the ionic binding group for the alternating polyelectrolyte layer.

Suitable pigments are available commercially as colloidally stable water dispersions from manufacturers such as Cabot, Clariant, DuPont, Dainippon and DeGussa. Particularly suitable pigments include those available from Cabot Corporation under the CAB-O-JET® name, for example 250C (cyan), 260M (magenta), 270Y (yellow) or 352K (black). The light absorbing (e.g. pigment) particles are typically surface treated to impart ionizable functionality. Examples of suitable ionizable functionality for light absorbing (e.g. pigment) particles include sulfonate functionality, carboxylate functionality as well as phosphate or bisphosphonate functionality. In some embodiments, surface treated light absorbing (e.g. pigment) particles having ionizable functionality are commercially available. For example, CAB-O-JET® pigments, commercially available from Cabot Corporation, sold under the trade names 250C (cyan), 260M (magenta), 270Y (yellow) and 200 (black), comprise sulfonate functionality. As yet another example, CAB-O-JET® pigments commercially available from Cabot Corporation, under the trade names 352K (black) and 300 (black), comprise carboxylate functionality.

When the light absorbing (e.g. pigment) particles are not pre-treated, the light absorbing (e.g. pigment) particles can be surface treated to impart ionizable functionality as known in the art.

Multiple light absorbing materials (e.g. pigments) may be utilized to achieve a specific hue or shade or color in the final product. When multiple light absorbing materials (e.g. pigments) are used, the materials are selected to ensure their compatibility and performance both with each other and with the optical product components.

In favored embodiments, the polyelectrolyte is prepared and applied to the microstructured surface as an aqueous solution. The term “aqueous” means that the liquid of the coating contains at least 85 percent by weight of water. It may contain a higher amount of water such as, for example, at least 90, 95, or even at least 99 percent by weight of water or more. The aqueous liquid medium may comprise a mixture of water and one or more water-soluble organic cosolvent(s), in amounts such that the aqueous liquid medium forms a single phase. Examples of water-soluble organic cosolvents include methanol, ethanol, isopropanol, 2-methoxyethanol, 3-methoxypropanol, 1-methoxy-2-propanol, tetrahydrofuran, and ketone or ester solvents. The amount of organic cosolvent typically does not exceed 15 wt-% of the total liquids of the coating composition. The aqueous polyelectrolyte composition for use in layer-by-layer self-assembly typically comprises at least 0.01 wt-%, 0.05 wt-% or 0.1 wt-% of polyelectrolyte and typically no greater than 5 wt-%, 4 wt-%, 3 wt-%, 2 wt-% or 1 wt-%.

In some embodiments, the aqueous solutions further comprise a “screening agent”, an additive that promotes even and reproducible deposition by increasing ionic strength and reducing interparticle electrostatic repulsion. Suitable screening agents include any low molecular weight salts such as halide salts, sulfate salts, nitrate salts, phosphate salts, fluorophosphate salts, and the like. Examples of halide salts include chloride salts such as LiCl, NaCl, KCl, CaCl₂, MgCl₂, NH₄Cl and the like, bromide salts such as LiBr, NaBr, KBr, CaBr₂, MgBr₂, and the like, iodide salts such as LiI, NaI, KI, CaI₂, MgI₂, and the like, and fluoride salts such as, NaF, KF, and the like. Examples of sulfate salts include Li₂SO₄, Na₂SO₄, K₂SO₄, (NH₄)₂SO₄, MgSO₄, CoSO₄, CuSO₄, ZnSO₄, SrSO₄, Al₂(SO₄)₃, and Fe₂(SO₄)₃. Organic salts such as (CH₃)₃CCl, (C₂H₅)₃CCl, and the like are also suitable screening agents.

Suitable screening agent concentrations can vary with the ionic strength of the salt. In some embodiments, the aqueous solution comprises (e.g. NaCl) screening agent at a concentration ranging from 0.01 M to 0.1M. The absorptive regions may contain trace amounts of screening agent.

After applying and drying the light absorbing coating to the (e.g. entire) surface of the microstructured film, the light absorbing coating is then removed from the top portions of the transmissive (e.g. protrusions) regions and also removed from the land regions, between the transmissive (e.g. protrusions) regions. It is appreciated that the LCF can have improved on-axis transmission (e.g. brightness) even when some of the light absorbing coating is retained.

Any suitable method can be used to selectively remove the light absorbing material from the top surface of the protrusions (e.g. light absorbing regions) and bottom surface of the channels.

In one embodiment, the light absorbing material is removed by reactive ion etching. Reactive ion etching (RIE) is a directional etching process utilizing ion bombardment to remove material. RIE systems are used to remove organic or inorganic material by etching surfaces orthogonal to the direction of the ion bombardment. The most notable difference between reactive ion etching and isotropic plasma etching is the etch direction. Reactive ion etching is characterized by a ratio of the vertical etch rate to the lateral etch rate which is greater than 1, Systems for reactive ion etching are built around a durable vacuum chamber. Before beginning the etching process, the chamber is evacuated to a base pressure lower than 1 Torr, 100 mTorr, 20 mTorr, 10 mTorr, or 1 mTorr. An electrode holds the materials to be treated and is electrically isolated from the vacuum chamber. The electrode may be a rotatable electrode in a cylindrical shape. A counter electrode is also provided within the chamber and may be comprised of the vacuum reactor walls. Gas comprising an etchant enters the chamber through a control valve. The process pressure is maintained by continuously evacuating chamber gases through a vacuum pump. The type of gas used varies depending on the etch process. Carbon tetrafluoride (CF₄), sulfur hexafluoride (SF₆), octafluoropropane (C₃F₈), fluoroform (CHF₃), boron trichloride (BCl₃), hydrogen bromide (IMO, chlorine, argon, and oxygen are commonly used for etching. RF power is applied to the electrode to generate a plasma. Samples can be conveyed on the electrode through plasma for a controlled time period to achieve a specified etch depth. Reactive ion etching is known in the art and further described in U.S. Pat. No. 8,460,568; incorporated herein by reference.

In some embodiments, the step of reactive ion etching results in the absorptive regions being narrower (less than the average width) near the bottom surface 311 of the channels. Removing the light absorbing material can result in a (e.g. slight) increase in the depth of the channels.

After removing the light absorbing coating from the bottom surface of the channels, the channels can be filled with an organic polymeric material. In some embodiments, the organic polymeric material is a polymerizable resin composition and the method further comprising (e.g. radiation) curing the polymerizable resin. Typically, the same polymerizable resin used in the manufacture of the microstructured film is utilized for filling the channels. Alternatively, a different organic polymeric material (e.g. polymerizable resin composition) is used. When a different organic polymer material (e.g. polymerizable resin composition) is used, the composition is typically selected to be index matched to the light transmissive regions. By “index matched”, it is meant that the difference in refractive index between the filling material and transmissive regions is typically less than 0.1 or 0.005. Alternatively, the channels may be filled with a different organic polymeric material (e.g. polymerizable resin composition) having a difference in refractive index of greater than 0.1. In yet another embodiment, the channels are not filled with an organic polymeric material (e.g. polymerized resin). In this embodiment, the channels typically comprise air, having a refractive index of 1.0.

When the channels are filled with a cured polymerizable resin, the light control film may optionally include cover film 470 bonded to the microstructured film with adhesive 410. When the channels are filled with air, the adhesive film and cover film are typically included.

In yet another embodiment, layer 410 may be a topcoat rather than adhesive. In this embodiment, cover film 470 may not be present.

FIG. 4 shows an LCF 400 that further includes an optional cover film 470 that can be the same, or different than, base layer 260. Optional cover film 470 can be bonded to the microstructured surface with an adhesive 410. Adhesive 410 can be any optically clear adhesive, such as a UV-curable acrylate adhesive, a transfer adhesive, and the like.

The LCF may further comprise other coatings typically provided on the exposed surface. Various hardcoats, antiglare coatings, antireflective coatings, antistatic, and anti-soiling coatings are known in the art. See for example U.S. Pat. Nos. 7,267,850; 7,173,778, PCT Publication Nos. WO2006/102383, WO2006/025992, WO2006/025956 and U.S. Pat. No. 7,575,847.

FIG. 5 shows a perspective schematic of a backlit display 500 according to one embodiment. Backlit display 500 includes an LCF 530 comprising transmissive regions 540 and absorptive regions 550 as previously described. Such LCF has a polar cut-off viewing angle θP, as previously described, of light leaving an output surface 590 of LCF 530. Backlit display 500 includes a light source 510 configured to transmit light through LCF 530, through an image plane 520, such as an LCD panel, and on to a viewer 595. The viewing angle at which the brightness is a maximum, can depend on the polar cut-off viewing angle as previously described.

Backlit display 500 can also include an optional brightness enhancement film 560 and a reflective polarizer film 570 to further improve the brightness and uniformity of the display. Brightness enhancement film can be a prism film, such as 3M™. Brightness Enhancement Film “BEF” or Thin Brightness Enhancement Film “TBEF”, available from 3M Company. Reflective polarizer film 570 can be a multilayer optical film, such as 3M™. Dual Brightness Enhancement Film “DBEF”, available from 3M Company, St. Paul, Minn. Brightness enhancement film 560 and reflective polarizer film 570, if included, can be positioned as shown in FIG. 5.

In other embodiments, the light control film comprising transmissive regions and absorptive regions, as previously described, can be bonded to an emissive (e.g. an organic light emitting diode, or OLED) display.

In some embodiments, the LCF described herein (i.e. a first LCF) can be combined with a second LCF. In some embodiments, the second LCF may be a LCF (e.g. privacy film) such described in U.S. Pat. Nos. 6,398,370; 8,013,567; 8,213,082; and 9,335,449. In other embodiments, the second LCF is an LCF as described herein (e.g. wherein the light absorbing regions have an aspect ratio of at least 30). The first and second LCFs can be stacked in various orientations.

In one embodiment, the first and second light control films are positioned such that the absorptive regions of the first LCF are parallel and typically coincident with the absorptive regions of the second LCF. In another embodiment, the first and second light control films are positioned such that the absorptive regions of the first LCF are orthogonal with the absorptive regions of the second LCF. The first and second light control films can also be positioned such that the absorptive regions range from being parallel to orthogonal with each other at a viewing angle of 0 degrees.

In some embodiments, the combination of first and second LCF has a relative transmission (e.g. brightness) of at least 60, 65, 70, 75, 80, 85, or 90% at a viewing angle of 0 degrees. In some embodiments, the relative transmission (e.g. brightness) at a viewing angle of +30 degrees, −30 degrees, or the average of +30 and −30 degrees is less than 25, 20, 15, 10, or 5%. In some embodiments, the average relative transmission (e.g. brightness) for viewing angles ranging from +35 to +80 degrees, −35 degrees to −85 degrees, or the average of these ranges is less than 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1%.

In some embodiments, this combination of LCF has a relative transmission (e.g. brightness) of at least 60, 65, 70, 75, 80, 85, or 90% at a viewing angle of 0 degrees. In some embodiments, the relative transmission (e.g. brightness) at a viewing angle of +30 degrees, −30 degrees, or the average of +30 and −30 degrees is less than 25, 20, 15, 10, or 5%.

When the channels are filled with air, the relative transmission (e.g. brightness) at higher viewing angles can be lower, and thus the film can exhibit improved privacy.

The light control films described herein are particularly useful as a component of a display device as a so-called hybrid privacy filter. The hybrid privacy filter may be used in conjunction with a display surface, wherein light enters the hybrid privacy filter on the input side of the light control film and exits the hybrid privacy filter or film stack at the color shifting film. A great number of electronic devices with displays may be used in conjunction with the present invention including laptop monitors, external computer monitors, cell phone displays, televisions, smart phones, automotive center information displays, automotive driver information displays, automotive side mirror displays (also referred to as e-mirrors), consoles, or any other similar LCD, OLED, micro-LED, or mini-LED based display. An additional benefit to applying hybrid privacy filters to a display is for contrast enhancement.

Other types of backlit display imaging devices are also contemplated, including non-electronic displays such as sunglasses, document coversheets, console switches in auto and aviation applications, airplane cockpit controls, helicopter cockpit controls, windows and any number of others.

In further embodiments, the light control film described herein can be useful as coverings for glass. For instance, the light control films may be laminated onto or within fenestrations. The fenestrations may be selected from a glass panel, a window, a door, a wall, and a skylight unit. These fenestrations may be located on the outside of a building or on the interior. They may also be car windows, train windows, airplane passenger windows, or the like. Advantages of incorporating these film stacks into fenestrations include reduced IR transmission (which may lead to increased energy savings), ambient light blocking, privacy, and decorative effects.

The present description should not be considered limited to the particular examples described herein, but rather should be understood to cover all aspects of the description as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the present description can be applicable will be readily apparent to those of skill in the art to which the present description is directed upon review of the instant specification. The foregoing description can be better understood by consideration of the embodiments shown by the testing results and examples that follow.

EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc., in the examples and in the remainder of the specification are by weight. Unless otherwise noted, all chemicals were obtained from, or are available from, chemical suppliers such as Sigma-Aldrich Co., St. Louis, Mo.

The following is a list of materials used throughout the Examples, as well as their brief descriptions and origins.

The components of Resin A used in the cast-and-cure microreplication process (Preparative Example 1) as well as the index-matched backfill material in Examples 2 and Examples 4-8 are listed in Table 1 below. The raw materials for the layer-by-layer coating are listed in Table 2 below. The raw materials for reactive ion etching are listed in Table 3 below.

TABLE 1 Raw materials for Resin A Material Abbreviation Source Aliphatic urethane diacrylate Photomer 6010 BASF Viscosity 5900 mPa · s at 60° C. Tensile Strength 2060 psi Tg = −7° C. Ethoxylated (10) bisphenol A SR602 Sartomer (Exton, PA) diacrylate Ethoxylated (4) bisphenol A SR601 Sartomer (Exton, PA) diacrylate Trimethylolpropane triacrylate TMPTA Cytec Industries (Woodland Park, NJ) Phenoxyethyl Acrylate PEA (Etermer 2010) Eternal Chemical Co., Ltd., Kaohsiung, Taiwan 2-Hydroxy-2-methylpropiophenone Darocur 1173 BASF Corporation (Florham photoinitiator Park, New Jersey) Diphenyl(2,4,6-trimethylbenzoyl)phosphine TPO BASF Corporation (Florham oxide photoinitiator Park, New Jersey) Irgacure 1035 anti-oxidant I1035 BASF Corporation (Florham Park, New Jersey)

TABLE 2 Raw materials for the layer-by-layer coatings Material Abbreviation Source Poly(diallyl-dimethyl PDAC Sigma-Aldrich Co. ammonium chloride), (St. Louis, molecular weight Missouri) 100-200K Polyethylenimine, molecular PEI Sigma-Aldrich Co. weight 25K (St. Louis, Missouri) Polyacrylic acid, molecular PAA Dow Chemical Company weight 100K, Accumer ™ (Midland, Michigan) 1510 CAB-O-JET ® 200 carbon COJ200 Cabot Corporation black nano-pigment, 130 nm (Boston, diameter, sulfonate Massachusetts) functionalized CAB-O-JET ® 250C cyan COJ250C Cabot Corporation nano-pigment, 91 nm (Boston, diameter, sulfonate Massachusetts) functionalized CAB-O-JET ® 260M magenta COJ260M Cabot Corporation nano-pigment, 105 nm (Boston, diameter, sulfonate Massachusetts) functionalized CAB-O-JET ® 352K carbon COJ352K Cabot Corporation black nano-pigment, (Boston, 70-80 nm diameter, Massachusetts) carboxylate functionalized Sodium chloride NaCl Sigma-Aldrich Co. (St. Louis, Missouri) Sodium hydroxide (1M in NaOH Avantor Performance water) Materials (Central Valley, PA)

TABLE 3 Raw materials for reactive ion etching Material Abbreviation Source Oxygen (UHP compressed O₂ Oxygen Service Company gas) (St Paul, Minnesota) Argon (UHP compressed gas) Ar Oxygen Service Company (St Paul, Minnesota)

Preparative Example 1 (PE1): Preparation of “Square Wave” Microstructured Film

A diamond (29.0 μm tip width, 3° included angle, 87 μm deep) was used to cut a tool having a plurality of parallel linear grooves. The grooves were spaced apart by a pitch of 62.6 microns.

Resin A was prepared by mixing the materials in Table 4 below.

TABLE 4 Composition of Resin A used to make microstructured film Material Parts by Weight Photomer 6010 60 SR602 20 SR601 4.0 TMPTA 8.0 PEA (Etermer 2010) 8.0 Darocur 1173 0.35 TPO 0.10 I1035 0.20

A “cast-and-cure” microreplication process was carried out with Resin A and the tool described above. The line conditions were: resin temperature 150° F., die temperature 150° F., coater IR 120° F. edges/130° F. center, tool temperature 100° F., and line speed 70 fpm, Fusion D lamps, with peak wavelength at 385 nm, were used for curing and operated at 100% power. The resulting microstructured film comprised a plurality of protrusions (e.g. light transmissive regions) separated by channels as illustrated in FIG. 2. The protrusions of the microstructured film are a negative replication of the grooves of the tool. The protrusions have a wall angle of 1.5 degrees resulting in the protrusions being slightly tapered (wider at the light input surface and narrower at the light output surface). The channels of the microstructured film are a negative replication of the uncut portions of the tool between the grooves.

Method for Making Layer-by-Layer Self-Assembled Coatings on Microstructured Film

Layer-by-layer self-assembled coatings were made using an apparatus purchased from Svaya Nanotechnologies, Inc. (Sunnyvale, Calif.) and modeled after the system described in U.S. Pat. No. 8,234,998 (Krogman et al.) as well as Krogman et al. Automated Process for Improved Uniformity and Versatility of Layer-by-Layer Deposition, Langmuir 2007, 23, 3137-3141.

The apparatus comprises pressure vessels loaded with the coating solutions. Spray nozzles with a flat spray pattern (from Spraying Systems, Inc., Wheaton, Ill.) were mounted to spray the coating solutions and rinse water at specified times, controlled by solenoid valves. The pressure vessels (Alloy Products Corp., Waukesha, Wis.) containing the coating solutions were pressurized with nitrogen to 30 psi, while the pressure vessel containing deionized (DI) water was pressurized with air to 30 psi. Flow rates from the coating solution nozzles were each 10 gallons per hour, while flow rate from the DI water rinse nozzles were 40 gallons per hour. The substrate to be coated was adhered with epoxy (Scotch-Weld epoxy adhesive, DP100 Clear, 3M Company, St. Paul, Minn.) to a glass plate (12″×12″×⅛″ thick) (Brin Northwestern Glass Co., Minneapolis, Minn.), which was mounted on a vertical translation stage and held in place with a vacuum chuck. In a typical coating sequence, the polycation (e.g., PDAC) solution was sprayed onto the substrate while the stage moved vertically downward at 76 mm/sec. Next, after a dwell time of 12 sec, the DI water solution was sprayed onto the substrate while the stage moved vertically upward at 102 mm/sec. The substrate was then dried with an airknife at a speed of 3 mm/sec. Next, the polyanion (e.g., pigment nanoparticles) solution was sprayed onto the substrate while the stage moved vertically downward at 76 mm/sec. Another dwell period of 12 sec was allowed to elapse. The DI water solution was sprayed onto the substrate while the stage moved vertically upward at 102 mm/sec. Finally, the substrate was then dried with an airknife at a speed of 3 mm/sec. The above sequence was repeated to deposit a number of “bi-layers” denoted as (Polycation/Polyanion)_(n) where n is the number of bi-layers.

Method for Reactive Ion Etching Microstructured Film

Reactive ion etching (RIE) was performed in a parallel plate capacitively coupled plasma reactor. The chamber has a central cylindrical powered electrode with a surface area of 18.3 ft². After placing the microstructured film on the powered electrode, the reactor chamber was pumped down to a base pressure of less than 1.3 Pa (2 mTorr). A mixture of Ar (argon) and O₂ (oxygen) gas was flowed into the chamber, each at a rate of 100 SCCM. Treatment was carried out using a plasma enhanced CVD method by coupling RF power into the reactor at a frequency of 13.56 MHz and an applied power of 6000 watts. Treatment time was controlled by moving the microstructured film through the reaction zone. Following the treatment, the RF power and the gas supply were stopped and the chamber was returned to atmospheric pressure. Additional information regarding materials, processes for applying cylindrical RIE, and further details around the reactor used can be found in U.S. Pat. No. 8,460,568 B2.

Method for Back-Filling Channels of the Microstructured Film

The channels were back-filled with Resin A used in PE1 by pipetting the resin between the microstructured film surface and a piece of unprimed, 2 mil-thick PET film placed on top, using a hand roller to apply pressure to the top PET film, and then UV curing with a Heraeus (Hanau, Germany) belt conveyer UV processor (Model #DRS(6)) with an ‘H’ bulb at 500 Watt power. Specifically, the samples were sent through the UV curing station three times at a conveyer speed of 50 ft/min. Next, the top PET film was stripped off the microstructured film by hand.

Method for Measuring the Luminance Profile from a Diffuse Light Source

A sample of film was placed on a Lambertian light source When the light transmissive regions are tapered, the film is positioned such that the widest portion of the tapered regions are closer to the light source. An Eldim L80 conoscope (Eldim S. A., HEROUVILLE SAINT CLAIR, France) was used to detect light output in a hemispheric fashion at all polar and azimuthal angles simultaneously. After detection, a cross section of transmission (e.g. brightness) readings were taken in a direction orthogonal to the direction of the louvers (denoted as a 0° orientation angle), unless indicated otherwise. Relative transmission (i.e. brightness of visible light) is defined as the percentage of on-axis luminance, at a certain viewing angle, between a reading with film and a reading without the film.

The Lambertian light source consisted of diffuse transmission from a light box having the baseline luminance profile depicted in FIG. 6. The light box was a six-sided hollow cube measuring approximately 12.5 cm×12.5 cm×11.5 cm (L×W×H) made from diffuse polytetrafluoroethylene (PTFE) plates of ^(˜)6 mm thickness. One face of the box was chosen as the sample surface. The hollow light box had a diffuse reflectance of ^(˜)0.83 measured at the sample surface (e.g. ^(˜)83%, averaged over the 400-700 nm wavelength range). During testing, the box was illuminated from within through a ^(˜)1 cm circular hole in the bottom of the box (opposite the sample surface, with the light directed toward the sample surface from inside). The illumination was provided using a stabilized broadband incandescent light source attached to a fiber-optic bundle used to direct the light (Fostec DCR-H with a 1 cm diameter fiber bundle extension from Schott-Fostec LLC, Marlborough Mass. and Auburn, N.Y.).

Method for Cross-Sectional Scanning Electron Microscopy (SEM)

Cross-sections were prepared via freeze fracturing using liquid nitrogen. SEM images were acquired with a Hitachi SU-8230 (Hitachi, Ltd., Tokyo, Japan) instrument.

Comparative Example 1-3 (CE1-CE-3) are Commercially Available Light Control Films Comparative Example 4 (CE4)

Two sections (each 3″×3″) of the film from CE1 were overlaid and laminated together with an optically clear adhesive (8171, 3M Company, St. Paul, Minn.). One sheet was oriented perpendicular to the other. That is, the original direction of the channels were offset by 90° between the top sheet and bottom sheet.

Preparative Example 2 (PE2): Preparation of Coating Solutions

PDAC was diluted from 20 wt % to a concentration of 0.32 wt % with deionized (DI) water. PAA was diluted from 25 wt % to a concentration of 0.1 wt %, and the pH was adjusted to 4.0 with 1M NaOH. CAB-O-JET® 200 (COJ200), CAB-O-JET® 250C (COJ250C), CAB-O-JET® 260M (COJ260M), and CAB-O-JET® 352K (COJ352K) were each diluted to a concentration of 0.10 wt % with DI water. NaCl was added to both the PDAC solution and pigment suspensions to a concentration of 0.05 M. 1M NaOH was added to the COJ352K suspension to a pH of 9. pH values were measured with a VWR (West Chester, Pa.) pH electrode (Catalog #89231-582), which was calibrated with standard buffer solutions.

Preparative Example 3 (PE3): Preparation of Cationic Pigment

Polyethylenimine (PEI)-modified CAB-O-JET® 352K (COJ352K) carbon black nanopigment, abbreviated as PEI-COJ352K, was prepared as follows. PEI (MW25K) was diluted to make a 10 wt % solution. A mass of 3.2 grams of the 10 wt % PEI solution was diluted with DI water up to a mass of 794.7 grams. Next, 5.3 grams of as-received COJ352K at 15.03% solids was added dropwise to the 794.7 gram PEI solution with vigorous magnetic stirring resulting in a final concentrations of 0.1 wt % COJ352K and 0.04 wt % PEI. Size and zeta potential of the polyethylenimine (PEI)-modified CAB-O-JET® 352K (COJ352K) were measured using a Brookhaven Instruments Corp. (Holtsville, N.Y.) ZetaPALS instrument with an aliquot of the PEI-COJ352K sample above diluted by 100× with 1 mM KCl. Particle size was described by d₁₀=77.5 nm, d₅₀=148.4 nm, and d₉₀=284.0 nm. Zeta potential was measured to be +37.9±0.9 mV.

Example 1 (EX1): Carbon Black Nano-Pigment, 130 nm Diameter, not Back-Filled

A sheet of microstructured film as made in PE1 was cut to a size of 9″×10″ and corona treated by hand using a BD-20AC Laboratory Corona Treater (Electro-Technic Products, Chicago, Ill.) to prevent the aqueous coating solutions from beading up and dewetting. PDAC and CAB-O-JET® ® 200 coating solutions were made as described in PE2. The corona-treated film was coated with (PDAC/COJ200)₁₀ using the “Method for Making Spray Layer-by-Layer Self-Assembled Coatings on Microstructured Film”. This coated film was subjected to reactive ion etching (RIE) at a power of 6000 W for a duration of 210 s. An equivalent coating deposited onto a glass plate had a thickness of 166 nm as measured with a Dektak XT stylus profilometer (Bruker Nano, Inc., Tucson, Ariz.) after scoring the coating with a razor blade. Based on the thickness of the equivalent coating deposited on glass, the aspect ratio of the louver was approximately 525:1.

Example 2 (EX2): Carbon Black Nano-Pigment, 130 nm Diameter, Back-Filled

A sheet of microstructured film as made in PE1 was cut to a size of 9″×10″ and corona treated by hand using a BD-20AC Laboratory Corona Treater (Electro-Technic Products, Chicago, Ill.) to prevent the aqueous coating solutions from beading up and dewetting. PDAC and CAB-O-JET® 200 coating solutions were made as described in PE2. The corona-treated film was coated with (PDAC/COJ200)₂₀ using the “Method for Making Spray Layer-by-Layer Self-Assembled Coatings on Microstructured Film”. This coated film was subjected to reactive ion etching (RIE) at a power of 6000 W for a duration of 210 s. Next, the channels were back-filled using the “Method for Back-Filling Channels of the Microstructured Film” described above. An equivalent coating deposited onto a glass plate had a thickness of 326 nm as measured with a Dektak XT stylus profilometer after scoring the coating with a razor blade.

Example 3 (EX3): Carbon Black Nano-Pigment, 70-80 nm Diameter, not Back-Filled

A sheet of microstructured film as made in PE1 was cut to a size of 9″×10″ and corona treated by hand using a BD-20AC Laboratory Corona Treater (Electro-Technic Products, Chicago, Ill.) to prevent the aqueous coating solutions from beading up and dewetting. PDAC and CAB-O-JET® 352K coating solutions were made as described in PE2. The corona-treated film was coated with (PDAC/COJ352K)₂₀ using the “Method for Making Spray Layer-by-Layer Self-Assembled Coatings on Microstructured Film”. The coated film was then subjected to reactive ion etching (RIE) at a power of 6000 W for a duration of 200 s. An equivalent coating deposited onto a glass plate had a thickness of 273 nm as measured by a Dektak XT stylus profilometer after scoring the coating with a razor blade.

Example 4-6 (EX4-6): Carbon Black Nano-Pigment, 70-80 nm Diameter, Back-Filled

Three sheets of microstructured film as made in PE1 were each cut to a size of 9″×10″ and corona treated by hand using a BD-20AC Laboratory Corona Treater (Electro-Technic Products, Chicago, Ill.) to prevent the aqueous coating solutions from beading up and dewetting. PDAC and CAB-O-JET® 352K coating solutions were made as described in PE2. Separate 9″×10″ pieces of the corona treated films were coated with (PDAC/COJ352K)₂₀, (EX4) (PDAC/COJ352K)₄₀ (EX5), and (PDAC/COJ352K)₆₀ (EX6) using the “Method for Making Spray Layer-by-Layer Self-Assembled Coatings on Microstructured Film”. The coated films were subjected to reactive ion etching (RIE) at a power of 6000 W for durations of 200 s (EX4) and 500 s (EX5 & EX6). Cross-sectional SEM images were taken of EX4, before and after RIE, but prior to back-filling. It was evident from the SEM images that the coating deposited on the film was of a uniform thickness and the thickness corresponded with the equivalent coating deposited onto glass, described below. Next, the channels were back-filled using the “Method for Back-Filling Channels of the Microstructured Film” described above. The luminance profile from a diffuse light source was measured using the “Method for Measuring the Luminance Profile from a Diffuse Light Source” above (data in FIG. 6 and Table 5). Equivalent coatings deposited onto glass plates had thicknesses of 273 nm (EX4), 536 nm (EX5), and 796 nm (EX6) as measured with a Dektak XT stylus profilometer after scoring the coatings with a razor blade. Based on the thickness of the equivalent coatings deposited on glass, the aspect ratios of the louvers ranged from approximately 109:1 (for EX6) to 319:1 (for EX4).

TABLE 5A Relative brightness (RB) for EX2, EX4-EX6 and CE2-CE3. % RB % RB % RB at +30° at −30° Avg. % # 0° viewing viewing viewing RB of +30° and −30° Ex. bilayers angle angle angle viewing angles EX2 20 86.6 17.9 21.8 19.9 EX4 20 91.0 21.6 19.4 20.5 EX5 40 91.9 21.9 19.0 20.4 EX6 60 91.0 17.8 14.8 16.3 CE2 N/A 68.1 23.1 12.8 17.9 CE3 N/A 64.3 13.6 4.8 9.2

TABLE 5B Relative brightness (RB) for EX2, EX4-EX6 and CE2-CE3. Average % RB for Average % RB for Average % RB for viewing angles % RB viewing angles viewing angles from +35° # 0° viewing from +35° from −35° to +80° and −35° Ex. bilayers angle to +80° to −80° to −80° EX2 20 86.6 4.49 5.05 4.77 EX4 20 91.0 5.12 4.82 4.97 EX5 40 91.9 4.54 4.25 4.40 EX6 60 91.0 3.14 3.01 3.08 CE2 N/A 68.1 3.47 3.43 3.43 CE3 N/A 64.3 1.56 1.06 1.31

Example 7 (EX7): Overlaid, Crossed Films

Two sections (each 3″×3″) of The light control film prepared according to EX4 were overlaid, with the structured sides facing each other, with one sheet being oriented perpendicular to the other. That is, the original direction of the channels was offset by 90° between the top sheet and bottom sheet. Resin A was dispensed between the two sheets and the two sheets were laminated together with a hand roller. The sample was cured as described in the “Method for Back-Filling Channels of the Microstructured Film”, and was measured using the “Method for Measuring the Luminance Profile from a Diffuse Light Source”. Data are in Table 6A and 6B.

Example 8 (EX8): Overlaid, Aligned Films

Two sections (each 3″×3″) of the light control film prepared according to EX4 were overlaid, with the structured sides facing each other, with one sheet being oriented parallel to the other. That is, the original direction of the channels was aligned between the top sheet and bottom sheet. Resin A was dispensed between the two sheets and the two sheets were laminated together with a hand roller. The sample was cured as described in the “Method for Back-Filling Channels of the Microstructured Film”, and was measured using the “Method for Measuring the Luminance Profile from a Diffuse Light Source”. Data are in Tables 6A-6C.

TABLE 6A Relative brightness measured for EX7-EX8 and CE4. % RB % RB % RB at +30° at −30° Avg. % 0° viewing viewing viewing RB of +30° and −30° Ex. angle angle angle viewing angles EX7 88.5 19.6 22.9 21.3 EX8 90.6 5.13 7.69 6.41 CE4 55.9 6.93 11.0 8.97

TABLE 6B Relative brightness measured for EX7-EX8 and CE4. Average % RB for Average % RB for Average % RB for viewing angles % RB viewing angles viewing angles from +35° 0° viewing from +35° from −35° to +80° and −35° Ex. angle to +80° to −80° to −80° EX7 88.5 4.48 4.97 4.73 EX8 90.6 1.01 1.14 1.08 CE4 55.9 0.68 0.93 0.81

TABLE 6C Relative brightness measured for EX7-EX8 and CE4. % RB % RB % RB at +30° at −30° Avg. % 0° viewing viewing viewing RB of +30° and −30° Ex. angle angle angle viewing angles EX7 88.5 19.1 19.1 19.1 EX8 90.6 90.4 88.9 89.6 CE4 55.9 6.66 12.8 9.73

TABLE 6D Relative brightness measured for EX7-EX8 and CE4. Average % RB for Average % RB for Average % RB for viewing angles % RB viewing angles viewing angles from +35° 0° viewing from +35° from −35° to +80° and −35° Ex. angle to +80° to −80° to −80° EX7 88.5 4.41 4.59 4.50 EX8 90.6 80.6 78.5 79.5 CE4 55.9 0.67 1.19 0.93

Example 9 (EX9): Cyan Nano-Pigment

A microstructured sheet of film as made in PE1 was cut to a size of 9″×10″ and corona Treated by hand using a BD-20AC Laboratory Corona Treater (Electro-Technic Products, Chicago, Ill.) to prevent the aqueous coating solutions from beading up and dewetting. PDAC and CAB-O-JET® 250C coating solutions were made as described in PE2. The corona-treated film was coated with (PDAC/COJ250C)₂₀ using the “Method for Making Spray Layer-by-Layer Self-Assembled Coatings on Microstructured Film”. This coated film was subjected to reactive ion etching (RIE) at a power of 6000 W for a duration of 150 s. Relative brightness was measured using the “Method for Measuring the Luminance Profile from a Diffuse Light Source” (data in Table 7). An equivalent coating deposited onto a glass plate had a thickness of 340 nm as measured by a Dektak XT stylus profilometer (Bruker Nano, Inc., Tucson, Ariz.) after scoring the coating with a razor blade.

Example 10 (EX10): Magenta Nano-Pigment

A microstructured sheet of film as made in PE1 was cut to a size of 9″×10″ and corona Treated by hand using a BD-20AC Laboratory Corona Treater (Electro-Technic Products, Chicago, Ill.) to prevent the aqueous coating solutions from beading up and dewetting. PDAC and CAB-O-JET® 260M coating solutions were made as described in PE2. The corona-treated film was coated with (PDAC/COJ260M)₂₀ using the “Method for Making Spray Layer-by-Layer Self-Assembled Coatings on Microstructured Film”. This coated film was subjected to reactive ion etching (RIE) at a power of 6000 W for a duration of 150 s. Relative brightness was measured using the “Method for Measuring the Luminance Profile from a Diffuse Light Source” (data in Table 7). An equivalent coating deposited onto a glass plate had a thickness of 313 nm as measured by a Dektak XT stylus profilometer (Bruker Nano, Inc., Tucson, Ariz.) after scoring the coating with a razor blade.

TABLE 7A Relative brightness for EX9-EX10 % RB % RB RIE % RB at +30° at −30° Avg. % # Time Resin 0° viewing viewing viewing RB of +30° and −30° Example bilayers (sec) Back-Filled? angle angle angle viewing angles EX9 20 150 No 85.7 26.3 24.0 25.1 EX10 20 150 No 95.8 43.7 44.5 44.1

TABLE 7B Relative brightness for EX9-EX10 Average % RB for Average % RB for Average % RB for viewing angles % RB viewing angles viewing angles from +35° 0° viewing from +35° from −35° to +80° and −35° Ex. angle to +80° to −80° to −80° EX9 85.7 10.8 10.0 10.4 EX10 95.8 30.4 31.1 30.8

Example 11 (EX 11): Cationic Pigment, Anionic Polyelectrolyte

A glass microscope slide (Fisher Scientific, Waltham, Mass.), 1″×3″ in size, was rinsed with DI water and isopropanol. The slide was mounted on a StratoSequence VI (nano Strata, Inc., Tallahassee, Fla.) automated layer-by-layer dip coater. The slide was dipped in the PEI-COJ352K solution described in PE3 for 1 min. Next the slide was dipped in three consecutive DI water rinse baths for 30 sec each. Next, the slide was dipped in a PAA solution (0.1 wt %, adjusted to pH 4 with HCl) for 1 min. Next, the slide was dipped in three consecutive DI water rinse baths for 30 sec each. The slide was rotated at 150 rpm in each bath. This cycle was repeated for a total of 10 times to deposit (PEI-COJ352K/PAA)₁₀. The coating had a thickness of 4 μm as measured with a Dektak XT stylus profilometer (Bruker Nano, Inc., Tucson, Ariz.) after scoring the coating with a razor blade. The microstructured film of PE1 could be layer-by-layer coated with this composition and subjected to RIE as previously described.

Example 12 (EX 12): Cationic Pigment, Anionic Pigment

A glass microscope slide (Fisher Scientific, Waltham, Mass.), 1″×3″ in size, was rinsed with DI water and isopropanol. The slide was mounted on a StratoSequence VI (nanoStrata, Inc., Tallahassee, Fla.) automated layer-by-layer dip coater. The slide was dipped in the PEI-COJ352K solution (as described in PE3) for 1 min. Next the slide was dipped in three consecutive DI water rinse baths for 30 sec each. Next, the slide was dipped in a COJ352K solution (as described in PE2) for 1 min. Next, the slide was dipped in three consecutive DI water rinse baths for 30 sec each. The slide was rotated at 150 rpm in each bath. This cycle was repeated for a total of 10 times to deposit (PEI-COJ352K/COJ352K)₁₀. The coating had a thickness of 240 nm as measured with a Dektak XT stylus profilometer (Bruker Nano, Inc., Tucson, Ariz.) after scoring the coating with a razor blade. The microstructured film of PE1 could be layer-by-layer coated with this composition and subjected to RIE as previously described. 

What is claimed is:
 1. A light control film, comprising: a light input surface and a light output surface opposite the light input surface; alternating transmissive regions and absorptive regions disposed between the light input surface and the light output surface, wherein the absorptive regions have an aspect ratio of at least 30 and the alternating transmissive region and absorptive regions have a relative transmission at a viewing angle of 0 degrees of at least 75%.
 2. The light control film of claim 1 wherein the absorptive regions have a width parallel to light input surface and a height orthogonal to the light input surface.
 3. The light control film of claims 1-2 wherein the alternating transmissive region and absorptive regions have a relative transmission at a viewing angle of +30 degrees or −30 degrees of less than 50, 45, 40, 35, 30, 25, 20, 10%, or 5%.
 4. The light control film of claims 1-3 wherein the alternating transmissive region and absorptive regions have an average relative transmission for viewing angles ranging from +35 to +80 degrees or an average relative transmission for viewing angles ranging from −35 to −80 degrees of less than 10, 9, 8, 7, 6, 5, 4, 3, or 2%.
 5. The light control film of claims 1-4 wherein the transmissive regions have a wall angle less than 5, 4, 3, 2, 1 or 0.1 degrees.
 6. The light control film of claims 1-5 wherein the transmissive regions and absorptive regions have a height ranging from 50 to 200 microns.
 7. The light control film of claims 1-6 wherein the absorptive region has an average width no greater than 5, 4, 3, 2, 1, 0.5, 0.25, or 0.10 microns.
 8. The light control film of claims 1-7 wherein the absorptive regions have an aspect ratio of at least 50, 100, 200, 300, 400, 500, 600, 700, 800 or
 1000. 9. The light control film of claims 1-8 wherein the absorptive regions have an average pitch of 10 to 200 microns.
 10. The light control film of claims 1-9 wherein the transmissive regions have an aspect ratio of at least 2, 3, 4, 5, 6, 7, 8, 9, or
 10. 11. The light control film of claims 1-10 wherein the absorptive regions comprise an organic light absorbing material.
 12. The light control film of claims 1-11 wherein the absorptive regions comprise light-absorbing particles having a median particle size less than 500 nanometers.
 13. The light control film of claims 1-12 wherein the absorptive regions comprise at least 25 wt.-% of light-absorbing particles.
 14. The light control film of claims 1-13 wherein the absorptive regions comprise polyelectrolytes.
 15. The light control film of claims 1-14 wherein the transmissive regions comprise a radiation cured (meth)acrylate polymer.
 16. The light control film of claims 1-15 wherein the alternating transmissive regions and absorption region are disposed on a base layer.
 17. The light control film of claims 1-16 wherein the light control film further comprises a cover film.
 18. The light control film of claims 1-16 wherein the light control film has a relative transmission at a viewing angle of 0 degrees of at least 75%.
 19. A light control film comprising a first light control film according to claim 1 disposed upon a second light control film.
 20. The light control film of claim 19 wherein the second light control film is according to claim 1 and the first and second light control films are positioned such that the absorptive regions range from being parallel to orthogonal with each other at a viewing angle of 0 degrees.
 21. The light control film of claim 20 wherein the second light control film is according to claim 1 and the first and second light control films are positioned such that the absorptive regions are coincident with each other at a viewing angle of 0 degrees.
 22. The light control film of claims 1-21 wherein the transmission is for a wavelength range of 400 to 700 nm.
 23. A microstructured film, comprising: a light input surface and a light output surface opposite the light input surface; alternating transmissive regions and absorptive regions disposed between the light input surface and the light output surface, wherein the absorptive regions have an aspect ratio of at least 30 and comprise an organic light absorptive material.
 24. The microstructured film of claim 23 wherein the microstructured film is further characterized by any one or combination of claims 2-22.
 25. A microstructured film, comprising: a light input surface and a light output surface opposite the light input surface; alternating transmissive regions and absorptive regions disposed between the light input surface and the light output surface, wherein the absorptive regions comprise a plurality of particles having a median particle size of less than 100 nanometers.
 26. A microstructured film comprising: a light input surface and a light output surface opposite the light input surface; alternating transmissive regions and absorptive regions disposed between the light input surface and the light output surface, wherein the absorptive regions comprise a polyelectrolyte.
 27. The microstructured film of claims 25-26 wherein the absorptive regions have an aspect ratio of at least
 30. 28. The microstructured film of claims 25-27 wherein the microstructured film is further characterized by any one or combination of claims 2-22.
 29. A method of making a light control film comprising: providing a microstructured film comprising a plurality of light transmissive regions alternated with channels, wherein the microstructured film has a surface defined by a top surface and side walls of the light transmissive regions and a bottom surface of the channels; applying an organic light absorptive material to the surface, and removing at least a portion of the light absorptive coating from the top surface of the light transmissive regions and bottom surface of the channels.
 30. The method of claim 29 wherein the organic light absorptive material comprises polyelectrolytes.
 31. The method of claims 29-30 wherein the organic light absorption material comprises a plurality of light absorbing particles.
 32. The method of claims 29-31 wherein the light absorbing particles have an average particle size of less than 500 nm.
 33. The method of claims 29-32 wherein the step of applying the light absorptive material comprises layer-by-layer self-assembly.
 34. The method of claims 29-33 wherein the step of removing the at least a portion of the light absorptive coating comprises reactive ion etching.
 35. The method of claims 29-34 further comprising filling the channel with an organic polymeric material.
 36. The method of claim 35 wherein the organic polymeric material comprises a polymerizable resin and the method further comprising curing the polymerizable resin.
 37. A method of making a microstructured film comprising: providing a microstructured film comprising a plurality of light transmissive regions alternated with channels, wherein the microstructured film has a surface defined by a top surface and side walls of the light transmissive regions and a bottom surface of the channels; applying a light absorptive material to the surface by layer-by-layer self-assembly; removing at least a portion of the light absorptive coating from the top surface of the light transmissive regions and bottom surface of the channels.
 38. The method of claim 37 wherein the material is a light absorptive material.
 39. The method of claims 37-38 wherein method further comprises removing at least a portion of the material from the top surface of the protrusions and bottom surface of the channels.
 40. The method of claims 37-39 wherein the method is further characterized by any one or combination of claims 30-36. 